AMBER Archive (2009)

Subject: [AMBER] Re: [q4md-fft] charge calculation

From: FyD (fyd_at_q4md-forcefieldtools.org)
Date: Mon Aug 17 2009 - 18:40:49 CDT

Subarna,

> I have  used the Gaussain 03 to calculate electrostatic potential..
> Single point calculation was performed  as geometry optimization
> couldnot be acheived as the system had transition metals.

You need to learn how to use your QM program for metal complexes.
Geometry optimization for organic structures is quite simple (SCF
computation "always" converges). For metal complexes this is another
story... I think computing MEP based on a non-optimized structure is
bad - in particular for metal complexes.

> My question is can I load this guassian output with ESP fits into
> the RED server to generate the RESP charges?. What changes I have
> to make in that case? I am attaching the gaussain ouput for your
> considerations.

In your case, I think the best bet is to modify the R.E.D. source code
so that you use the theory level you wish. This means:
- Replace HF by the theory level of your choice.
- Use the Gen keyword in Gaussian (if you need it).
- Modify other parameters...
We have already done that & this is quite simple to do in PERL/R.E.D.
(we are going to release a RESP charge model for metal complexes in
R.E.D. Server).

Finally, I do not think this is straightforward loading a MEP in
R.E.D. as input... A better choice would be to load the geometry
optimization output in R.E.D. as input, and let R.E.D. compute the MEP
using the theory level you selected/implemented.

Do not hesitate to modify the source code of R.E.D...

regards, Francois

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